Method and device to control the gain of a radio receiver

ABSTRACT

An automatic gain control (AGC) method and system for a radio receiver are proposed in which the ACG comprises two AGC loops; a first loop controlling signal gain in the analogue portion of the radio receiver, a second loop controlling gain in the digital domain after digitization of the received signal. The analogue AGC loop has a slower response time than the digital AGC loop. When applied to a multi-branch diversity receiver, each branch has its own digital AGC loop, but the analogue gain can be common to all branches, based on measurement of the analogue signal in each branch.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/127,941, filed Jul. 28, 2011 (35 U.S.C. §371(c) date), which is theNational Stage of International Application No. PCT/EP2009/064671, filedNov. 5, 2009, which claims priority under 35 U.S.C. §119 to EuropeanPatent Application No. EP 08305787.7, filed on Nov. 7, 2008. U.S.application Ser. No. 13/127,941 and European Patent Application No. EP08305787.7 are both hereby incorporated herein by reference in theirentireties.

The present disclosure relates to signal processing in radio receiversand in particular to an automatic gain control (AGC) system and methodin which the effects of DC current transients on system performance arereduced.

Reception of radio signals in a radio apparatus configured therefore anddown converting the desired receiving signal from the radio frequency(RF) band into the baseband can generally be done in different ways. Acommon way is to convert the RF signal down to an intermediate frequency(IF) and in a second step to convert the resulting signal down into thebaseband. The converting operation is usually done by a well-knownmixing operation with a suitable mixing frequency. For cost reduction,in zero IF receivers, which are broadly used in wireless systems, downconversion from the RF receiving signal to the baseband is done directlywithout the intermediate frequency step. One drawback in zero-IFreceivers is the presence of a residual direct current (DC) offset afterthe down conversion of the receiving signal, wherein self-mixing of thelocal oscillators and/or second order intermodulation of the employedmixers creates DC offsets in the baseband signal. Further, even-orderdistortions may convert strong interfering signals to baseband.Furthermore, 1/f noise being inherent in all semiconductor devices andbeing inversely proportioned to the frequency (f) may mask the basebandsignal. Moreover, direct conversion receivers put high demands on thebaseband signal processing components because gain control and filteringmust be done at baseband frequency range.

In modern receiver architectures, the analog RF receiving signal isconverted from the analog domain into the digital domain for furtherprocessing, since digital signal processing is available with highperformance and at low cost. In order to match the signal dynamicsrequired by the system before and after the used analogue-to-digitalconverters (ADC), an automatic gain control (AGC) system could be usedfor control of amplification gain for the receiving signal in the one ormore signal amplifiers located in the reception path.

The DC offset may be quite large causing saturation of the ADC, e.g.leading to loss of dynamics, and other problems in the receiver. To copewith these effects, so called DC offset compensation circuits aregenerally employed in the reception (RX) path of radio receivers.Basically, a simple example for DC offset cancellation is application ofcapacitors, connected in series into the signal path and thus blockingpropagation of DC signals. A more complex approach is an active highpass filter configured to remove the unwanted DC components inherent toself-mixing products.

Usually, AGC is implemented by a respective gain control algorithm. Dueto the digital nature of most AGC systems, also the analogue gain, i.e.in the receiving path before the ADC, is adjusted by changing the gainof the respective amplifiers in a stepwise manner, i.e. the gain iscontrolled in discrete gain steps. However, switching of the gain in thesignal path generates DC transients in the DC offset, which from afrequency spectrum point of view contain higher frequency components,which cannot be filtered or cancelled by the DC offset compensation orcancellation circuits.

Thus, even that the DC compensation is permanently active, DC transientsoccur at gain step transitions; every time these gain steps are toggled.Moreover, these transients are heavily RF architecture dependent. Theirsettling time and peak voltage depend on a variety of RF IC architectureparameters, such as the impedance of the receiving gain chain, thelocation of the AGC loops with regards to amplifier gain locations andthe weight of the gain step.

For instance, link level simulations for UMTS release 5, HSDPA, haveshown that DC transients in the order of the frame rate caused by theAGC loop degrade the throughput versa system performance of baseband(BB) integrated circuit (IC), e.g. the signal to noise ratio (SNR).

U.S. 2005/0208916 A1 discloses a direct down conversion receiverarchitecture comprising a digital variable gain amplifier (DVGA), anautomatic gain control (AGC) loop to provide gain control for the DVGAand RF/analog circuitry, and a serial bus interface (SBI) unit toprovide controls for the RF/analog circuitry via a serial bus.

U.S. 2003/0199264 A1 discloses a system and method for a fast acquiringDC offset cancellation by increasing high pass loop bandwidth andadjusting DC offset levels at baseband. Afterwards the high pass loopbandwidth is decreased in order to fine-tune the previous estimate andto remove small variation in DC.

In view of the foregoing, a method and a system are proposed allowing areduction of effects of DC current transients on receiver systemperformance.

According to a first aspect, an automatic gain control system for aradio receiver is proposed, this system having at least one receivingsignal path with an analogue and a digital portion.

According to a general feature, the AGC system comprises at least twoAGC loops, wherein at least one first AGC loop is configured to controlthe gain of at least one signal amplifier in the analogue portion of thereceiver and has a first cycle time; wherein at least one second AGCloop is configured to control signal amplification of at least onesignal processing unit in the digital portion of the receiver and has asecond cycle time, and wherein the second cycle time is shorter than thefirst cycle time.

In certain embodiments, the first cycle time is by orders of magnitudelonger than the second cycle time.

In other embodiments, for example if there is no frequent variation ofsignal reception conditions expected, the first cycle time might not beused at all, but only actually appearing variation of receptionconditions lead to a gain control in the analogue portion of thereceiver.

In certain embodiments the radio receiver is a multi-branch receiver,which comprises a plurality of generally similar receiving signal paths,each path being equipped with at least two AGC loops, i.e. at least onearranged in the analogue portion and the at least one other arranged inthe digital portion of the respective receiving signal paths of thereceiver.

Accordingly, according to another feature of the AGC, the radio receiveris a multi-branch receiver having at least two parallel receiving signalpaths, each receiving signal path comprises at least one first AutomaticGain Control loop and at least one second Automatic Gain Control loop.

In certain embodiments, the arrangement of the multi-branch receiver maybe part of a diversity receiver, which operates several antennas forenhancing signal reception capability.

In a further development, the gain of the receiving signal amplificationin the analogue portion of each receiving signal path is set orcontrolled by means of the same gain control signal. For example, in adual branch diversity receiver, each branch has its own digital AGCloop, but the analogue gain can be arranged as common for both branches,based on measurement of the analogue signal in each branch. Thisadvantageously enables reduction of hardware and firmware (FW) orsoftware (SW), i.e. the embedded code in the baseband, complexity andthus reduces e.g. costs and weight.

The basic idea of the AGC system resides in the perception that DCtransients due to gain step transitions in the analog AGC system inradio receivers reduce system performance. The present disclosureprovides an improved AGC system and a respective AGC method, by whichsusceptibility of radio receivers to such DC transients is remarkablyreduced. This is achieved by combining at least two AGC loops in theradio receiver signal path, where a first loop is arranged forcontrolling gain in the analogue domain of the receiver and a secondloop is arranged for controlling gain in the digital domain after A/Dconversion, i.e. digitization of the received signal. By configuring theanalogue AGC loop with a substantial slower cycle time than the digitalAGC loop, the occurrence of DC transients can be effectively reduced.

For example, the system is located in a receiving signal path of amobile communication device or a mobile station.

The mobile communication device or station may thus comprise a receiverfor at least one of a wireless communication systems, wireless localloops, wireless LAN applications, and/or cellular systems in accordancewith at least one of the following communication standards UMTS, WCDMA,UTRATDD, UTRAFDD, TDSCDMA, CDMA2000, and OFDMA.

For example, the mobile communication device or station is a devicecapable for High Speed Downlink Packet Access.

According to a second aspect, it is herby proposed a method forAutomatic Gain Control (AGC) in a radio receiver having at least onereceiving signal path with an analogue and a digital portion, the methodcomprising

-   -   at least one first amplifying step, in which an analogue        receiving signal is amplified in the analogue portion,    -   digitizing the amplified analogue receiving signal into a        digitized receiving signal;    -   at least one second amplifying step, in which the digitized        receiving signal is amplified in the digital portion,    -   controlling a first gain for said first amplifying step based on        a first cycle time (t1), and    -   controlling a second gain for said second amplifying step based        on a second cycle time (t2),

wherein the second cycle time is shorter than first cycle time.

According to another feature, the method comprises processing of severalreceiving signals in a multi-branch receiver having at least twoparallel receiving signal paths, the step of controlling the first gaincomprising determining one common gain control value in each branch.

For example the second cycle time is by orders of magnitude shorter thanthe first cycle time.

The method may further comprise controlling the first gain independentlyof the first cycle time based on determining if there is a predeterminedchange in receiving conditions.

According to a further aspect, it is hereby proposed a computer programcomprising program instructions, which, when performed on a programmableprocessor, cause the processor to perform the steps of a method asdefined above.

Preferred embodiments and further developments of the present disclosurearc defined in the dependent claims of the independent claims. It shallbe understood that the apparatus and the method of the presentdisclosure have similar and/or identical preferred embodiments andadvantages.

These and other aspects will be apparent from and elucidated withreference to the embodiment(s) described hereinafter. In the followingdrawings, the figures are schematically drawn and not true to scale, andidentical reference numerals in different figures, if any, may refer tocorresponding elements. It will be clear for those skilled in the artthat alternative but equivalent embodiments are possible withoutdeviating from the true inventive concept.

FIG. 1 illustrates an example of a signal path in an embodiment of radioreceiver of the first aspect;

FIG. 2 shows a time diagram, illustrating DC offset variation during again adjustment operation by the Automatic Gain Control (AGC), causingDC transients;

FIG. 3 is a flow chart illustrating the processing of two AGC loops; and

FIG. 4 shows a further embodiment of a radio receiver applied to adual-branch receiver.

The higher the update rate of an AGC loop controlling gain in ananalogue portion of a transfer path, the higher is the occurrence orfrequentness of DC transients caused by change of the amplification gainof the received analogue signal containing DC offset.

The present disclosure proposes an improvement to the AGC system andrespective AGC method in a radio receiver aiming on a significantreduction of such DC transients in the receiving signal.

This is accomplished by, basically, employing at least two separate AGCloops in the radio receiver signal path. The at least one first AGC loopis configured to control solely signal amplification in the analogueportion of the signal path. According to the herein presented solution,a first cycle rate of the first AGC loop defines the time span betweentwo possible amplification adaptations, i.e. between two possible DCtransients. Preferably, the first cycle time is predefined in order tomatch particular system requirements. For example, the cycle time can bemade dependent on the propagation conditions. That is to say, the systemmay be configured to adapt the cycle time automatically to apredetermined longer value if propagation conditions are static or to apredetermined shorter value in case of multi-path fading conditions. Forinstance, for the assumption of 3G UMTS environment, under multi-pathfading conditions, e.g. two path with about 3 km/h, as cycle time of oneUMTS frame, i.e. 10 ms, or one slot, i.e. 667 ms, may be used. Further,for static propagation conditions a cycle time of 20 UMTS frames, i.e.200 ms, or even more may be applied.

The at least one second AGC loop is configured to control signalamplification in the digital portion of the signal path. According tothe herein presented solution, this second AGC loop has a second cycletime, which is defined independently from the first cycle time.According to the present disclosure, the analogue first AGC loop has asubstantial longer cycle time than the second digital AGC loop.

FIG. 1 illustrates a schematic block diagram of a receiving signal pathof a radio receiver in accordance with a first embodiment. An antenna20, for reception of a radio frequency signal of interest, is followedby a radio frequency (RF) receiving signal amplifier 21, e.g. a lownoise amplifier (LNA). The amplifier 21 is followed by an analogue todigital converter (ADC) 22.

After the ADC 22, the receiving signal passes a filter 23, e.g. a raisedcosine filter (RRC) filter, and a scaler 24 before supplied to anequalizer 25.

Based on the output of the ADC 22, a Pre-Filter RRSS detector 26,detects the signal level of the output of the ADC 22 and/or receives anoutput of the ADC 22 which indicates if the ADC 22 is saturated by theinput signal. Pre-(filter)-RRSS detector 26 is configured to measure therelative receive signal strength (RRSS) of the received (Rx) I/Qbaseband signal. Detector 26 measures the I/Q signal received after theADC 22 as AGC analog loop related measurement, and thus named Pre-RRSSor Pre-RRC (with reference to the RRC filter). The detector 26 providesan input signal to a slow first AGC loop AGC1. The slow first AGC loopAGC1 operates a serial peripheral interface SPI RF, e.g. a 3-wire buswhich vehicles the control words for the radio transceiver, control 27controlling the radio frequency amplifier 21 by a first gain controlsignal G1.

After the scaler 24 is a post-(filter)-RRSS detector 28, which providesan input signal to a fast second ACC loop ACC2. Again thepost-(filter)-RRSS detector is configured to measure the Rx digital 1/Qbaseband signal strength received after the scaler 24. Detector 28measures the root-raised cosine filtered baseband signal as AGC digitalloop related measurement, thus also named post-RRSS or post-RRC (withreference to the RRC filter). The fast second AGC loop AGC2 controls thedigital implemented gain in the scaler 24 by a gain control signal G2.

Referring now to FIG. 2 the principle of DC offset compensation timingis discussed. FIG. 2 shows a schematic timing diagram, illustratingvarying DC offset current 30 in a radio receiver with a stepwise gaincontrol. At a first point in time 31 the analogue signal amplificationis toggled boosting the DC share of the signal. This boost containsaccording to Fourier analysis a large plurality of frequencies notoriginating from and not associated with the received signal but nowpropagated via the same transfer path leading to interference and noise.

Further, until the existing DC offset compensation means lower the DCoffset current, during time span 32 electric power is wasted, signaldynamic is reduced and generally unwanted heat is produced within thedevice. Depending on characteristics of the existing DC offsetcompensation means the graph may look different and thus the impact tothe signal may also differ from that depicted in FIG. 2. Nevertheless,the discussed effects generally exist and applying the present teachingcan reduce their occurrence frequency.

Now with reference to FIG. 3, the operation of the AGC system will beexplained in more detail. Thus, FIG. 3 shows a flow chart of the AGCmethod, which can be implemented in a respective radio receiver. Note,in the flow chart at steps where a condition is checked, “0” correspondsto “NO” and “1” corresponds to “YES”.

It goes without saying that the method steps described in the followingcan be implemented by means of a programmable processor, where themethod steps are coded by means of program code instructions, which whenrun on the processor, cause the processor to perform the steps of theAGC method.

At the beginning of the AGC algorithm, at step S100, a timer T1 isstarted for the first cycle rate or time for control of the firstanalogue AGC loop, i.e. the slow AGC loop AGC1.

The signal gain in at least one amplifier located in the analogueportion of the receiving signal path is adjusted in step S200 inaccordance with a certain criteria, e.g. such as based on the result ofchecking whether the ADC 22 is saturated or not.

Then, in step S300 it is judged whether the amplified receiving signalis in the dynamic range of the receiver or not. If not, the procedurereturns to step S200, where a gain adjustment is done. That is to say,the adjustment loop is passed until analogue signal gain matches thedynamic range of the receiver.

Now, until further notice, in step S400 the first analogue AGC loop isdeactivated. Hence, no further DC transients will be generated in theanalog domain.

Next, in step S500 a second timer T2 for timing of the second cycle rateor time of the second digital AGC loop AGC2 is started.

In step S600 the signal gain in at least one unit of the digital portionof the receiving signal path is adjusted. In the following step S700 acheck is done whether in the meantime an important or significant changein the receiving conditions of the receiving signal has happened, whichcannot be coped with by the second digital AGC loop alone. Thus, a gainadjustment is required in the first analog AGC loop, i.e. in theanalogue portion of the radio receiver.

If so (YES), the procedure goes to step 5800, where the analogue AGCloop is reactivated again.

In the other case (NO), the status of the first timer T1 is checked instep S900. If the first timer T1 has expired (YES), i.e. the first cycletime period is over, the procedure continues at step S800. In otherwords, the analogue AGC loop is reactivated again in step S800regardless of the actual set gain control value G1.

If the first timer T1 has not expired (NO), then in step S1000 thesecond timer T2 is checked. In the case that the second timer T2, i.e.the second cycle time period is over (YES), the second digital AGC loopis recurred by a return of the AGC procedure to step S500.

If the second timer T2 has not expired (NO), then the AGC procedure goesto step S900 and the first timer T1 is again checked in step S900.

It should be noted that FIG. 3 in connection with the description aboveillustrates only one particular embodiment by way of an example. It goeswithout saying, that the herein disclosed principle can be varied ormodified without deviating from the scope of the present disclosure. Forinstance, the timer T1 could be left and only one time could be used forboth AGC loops, implemented by a central AGC control unit. Then, onlydetection of an important change in reception conditions would returnthe algorithm back into the analogue gain adjustment in steps S200 andS300. Also disabling S400 and enabling S800 the analogue AGC loop couldbe dropped without departing from the herein described principle.

In further development the herein disclosed AGC system can beimplemented into each branch of a multi-branch radio receiver, e.g. suchas a diversity receiver. In this case, each receiving signal path orbranch between one antenna 20 or more antennas and the equalizer 25comprises the at least two separate AGC loops which operateindependently of one another. Such an application of the AGC system andmethod is in particular useful for spatial diversity reception.

Moreover, in still another further development, the receiver comprisesat least two parallel receiving signal paths, where the respective atleast two analogue amplifiers in each receiving signal branch may becontrolled by one single, i.e. common, amplification gain control signalor factor, respectively, based on measurement of the analogue signal ineach branch or path.

FIG. 4 shows an embodiment of such multi-branch receiver architecture asa further development, where two basically identical receiving signalbranches or paths, as illustrated in FIG. 1, are arranged in parallel.The receiving signal branches and share parts of the first analog AGCloop. That is to say, the first automatic gain control AGC1 is a commonentity located in the analogue portion and the SPI RF control 27controls amplification of both receiving signal paths. The otherelements of the two branches remain separate and keep operatingindependently, i.e. the operation is in principle the same as describedin connection with FIGS. 1 to 3.

Accordingly, hardware (HW) complexity can be reduced regarding not onlythe number of HW pins, but also by reducing the digital RF controlinterface and FW or SW complexity. For instance, only two sets of threewire-buses, i.e. six control lines altogether are required. Thus, thenovel AGC architecture allows simplification of the HW RF-Bbi interfaceof a HSDPA system, where by means of a single common three wire bus maybe used to control the two radios. In preferred embodiments the presentdisclosure is implemented in a mobile station. As mentioned aboveparticularly wireless devices comprising zero-IF receivers benefit fromefficient DC offset compensation. Especially battery powered devicesbenefit from reduced power looses by DC offset compensation. Thusbattery life cycles and user's mobility are not unnecessarily shortened.

Possible applications for the present principle are in receivers forwireless communication systems, including wireless local loops, wirelessLAN applications, and cellular systems such as 3G UMTS, i.e. WidebandCode Division Multiple Access (WCDMA) both UMTS Terrestrial Radio AccessTime Division Duplex (UTRATDD) and UMTS Terrestrial Radio AccessFrequency Division Duplex (UTRAFDD), Time Division-Synchronous CodeDivision Multiple Access (TDSCDMA), CDMA2000, Orthogonal FrequencyDivision Multiple Access (OFDMA) systems. These receivers are common inmobile stations being capable of operating in cellular communicationnetworks.

It shall be appreciated, that examples and embodiments of the presentdisclosure discussed above shall only aid in understanding and using theabove description and many variations will be apparent to those skilledin the art that can be applied without departing from the scope of thisdisclosure as defined in the appended claims.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; thedisclosure is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the disclosure, from a study of thedrawings and the appended claims. In the claims, the word “comprising”does not exclude other elements or steps, and the indefinite article “a”or “an” does not exclude a plurality. A single means or other unit mayfulfill the functions of several items recited in the claims. The merefact that certain measures are recited in mutually different dependentclaims does not indicate that a combination of these measured cannot beused to advantage. Any reference signs in the claims should not beconstrued as limiting the scope.

The invention claimed is:
 1. An Automatic Gain Control system for aradio receiver having at least one receiving signal path with ananalogue and a digital portion, the Automatic Gain Control systemcomprising: at least two Automatic Gain Control loops; wherein at leastone first Automatic Gain Control loop comprises a first AGC circuit andis configured to initially control the gain of at least one signalamplifier located in the analogue portion of the receiver and thereafterto control the gain of the at least one signal amplifier located in theanalogue portion of the receiver only upon detection of a change inreception conditions that satisfies predetermined criteria; wherein atleast one second Automatic Gain Control loop comprises a second AGCcircuit and is configured to control the signal amplification of the atleast one signal processing unit in the digital portion of the receiver;and wherein the digital portion of the receiver operates on a digitizedreceiving signal that is a digitized form of an amplified analoguereceiving signal produced by the analogue portion of the receiver. 2.The system according to claim 1, wherein the radio receiver is amulti-branch receiver having at least two parallel receiving signalpaths, and wherein each receiving signal path comprises at least onefirst Automatic Gain Control loop and at least one second Automatic GainControl loop.
 3. The system according to claim 2, wherein in eachreceiving signal path the at least one first Automatic Gain Control loopis set by means of the same gain control signal.
 4. The system accordingto claim 1, wherein the system is located in a receiving signal path ofa mobile communication device or a mobile station.
 5. The systemaccording to claim 4, wherein the mobile communication device or stationcomprises a receiver for at least one of a wireless communicationsystems, wireless local loops, wireless LAN applications, and/orcellular systems in accordance with at least one of the followingcommunication standards UMTS, WCDMA, UTRATDD, UTRAFDD, TDSCDMA,CDMA2000, and OFDMA.
 6. The system according to claim 4, wherein themobile communication device or station is a device capable for HighSpeed Downlink Packet Access.
 7. The Automatic Gain Control system ofclaim 1, wherein the predetermined criteria include a detection that thechange in reception conditions cannot be coped with solely bycontrolling a signal amplification of at least one signal processingunit in the digital portion of the receiver.
 8. The Automatic GainControl system of claim 1, wherein the at least one first Automatic GainControl loop is configured to periodically detect whether the change inreception conditions cannot be coped with solely by controlling thesignal amplification of the at least one signal processing unit in thedigital portion of the receiver.
 9. The Automatic Gain Control system ofclaim 1, wherein: the second Automatic Gain Control loop has a secondcycle time; and the at least one first Automatic Gain Control loop isconfigured to periodically detect, at a rate based on the second cycletime, whether the change in reception conditions cannot be coped withsolely by controlling the signal amplification of the at least onesignal processing unit in the digital portion of the receiver.
 10. Amethod for Automatic Gain Control (AGC) in a radio receiver having atleast one receiving signal path with an analogue and a digital portion,the method comprising: at least one first amplifying step, in which ananalogue receiving signal is amplified in the analogue portion, whereinthe analog portion comprises a first AGC circuit in a first feedbackloop; digitizing the amplified analogue receiving signal into adigitized receiving signal; at least one second amplifying step, inwhich the digitized receiving signal is amplified in the digitalportion, wherein the digital portion comprises a second AGC circuit anda second feedback loop; initially controlling a first gain for saidfirst amplifying step and thereafter controlling the first gain for saidfirst amplifying step only upon detection of a change in receptionconditions that satisfies predetermined criteria; and controlling thesecond gain for said second amplifying step.
 11. The method according toclaim 10, wherein the method comprises processing of several receivingsignals in a multi-branch receiver having at least two parallelreceiving signal paths, and wherein the step of controlling the firstgain comprises determining one common gain control value in each branch.12. The method of claim 10, wherein the predetermined criteria include adetection that the change in reception conditions cannot be coped withsolely by controlling a second gain for said second amplifying step. 13.The method of claim 10, comprising: periodically detecting whether thechange in reception conditions cannot be coped with solely bycontrolling a second gain for said second amplifying step.
 14. Themethod of claim 13, wherein: controlling the second gain for said secondamplifying step is based on a second cycle time; and periodicallydetecting whether the change in reception conditions cannot be copedwith solely by controlling the second gain for said second amplifyingstep is performed based on the second cycle time.
 15. A nontransitoryprocessor-readable storage medium comprising program instructions that,when performed on a programmable processor, cause the programmableprocessor to perform a method for Automatic Gain Control (AGC) in aradio receiver having at least one receiving signal path with ananalogue and a digital portion, the method comprising: at least onefirst amplifying step, in which an analogue receiving signal isamplified in the analogue portion, wherein the analog portion comprisesa first AGC circuit in a first feedback loop; digitizing the amplifiedanalogue receiving signal into a digitized receiving signal; at leastone second amplifying step, in which the digitized receiving signal isamplified in the digital portion, wherein the digital portion comprisesa second AGC circuit and a second feedback loop; initially controlling afirst gain for said first amplifying step and thereafter controlling thefirst gain for said first amplifying step only upon detection of achange in reception conditions that satisfies predetermined criteria;and controlling the second gain for said second amplifying step.
 16. Thenontransitory processor-readable storage medium of claim 15, wherein thepredetermined criteria include a detection that the change in receptionconditions cannot be coped with solely by controlling a second gain forsaid second amplifying step.
 17. The nontransitory processor-readablestorage medium of claim 15, wherein the method comprises: periodicallydetecting whether the change in reception conditions cannot be copedwith solely by controlling a second gain for said second amplifyingstep.
 18. The nontransitory processor-readable storage medium of claim17, wherein: controlling the second gain for said second amplifying stepis based on a second cycle time; and periodically detecting whether thechange in reception conditions cannot be coped with solely bycontrolling the second gain for said second amplifying step is performedbased on the second cycle time.
 19. An Automatic Gain Control (AGC)system for a radio receiver having at least one received signal pathwith a first portion having an output coupled to an input of a secondportion, wherein the first portion comprises a first signal amplifierand the second portion comprises a second signal amplifier, theAutomatic Gain Control system comprising: a first AGC circuitcomprising: a detector configured to receive an output signal of thefirst portion and to detect a signal reception condition based on theoutput signal of the first portion; and circuitry coupled to receive adetection output from the detector and configured to initially control again of the first signal amplifier located in the first portion of thereceiver and thereafter to control the gain of the first signalamplifier in response to detection of a change in reception conditionsthat satisfies predetermined criteria, wherein the predeterminedcriteria include the change in reception conditions being of a magnitudesuch that the change in reception conditions cannot be coped with by asecond AGC circuit that controls a gain of the second signal amplifier.20. An Automatic Gain Control (AGC) system for a radio receiver havingat least one received signal path with a first portion having an outputcoupled to an input of a second portion, wherein the first portioncomprises a first signal amplifier and the second portion comprises asecond signal amplifier, the Automatic Gain Control system comprising: afirst AGC circuit comprising: a detector configured to receive an outputsignal of the first portion and to detect a signal reception conditionbased on the output signal of the first portion; and circuitry coupledto receive a detection output from the detector and configured toinitially control a gain of the first signal amplifier located in thefirst portion of the receiver and thereafter to control the gain of thefirst signal amplifier in response to detection of a change in receptionconditions that satisfies predetermined criteria, wherein the first AGCcircuit further comprises circuitry configured to control the gain ofthe first signal amplifier in response to a detection that a first cycletime period has expired.
 21. A radio receiver having at least onereceiving signal path with a first portion having an output coupled toan input of a second portion, wherein the first portion comprises afirst signal amplifier and the second portion comprises a second signalamplifier, the radio receiver comprising: a detector configured todetect a signal reception condition; and an Automatic Gain Controlsystem, wherein the Automatic Gain Control system comprises: a first AGCcircuit comprising: circuitry coupled to receive a detection output fromthe detector and configured to initially control a gain of the firstsignal amplifier located in the first portion of the receiver andthereafter to control the gain of the first signal amplifier in responseto detection of a change in reception conditions that satisfiespredetermined criteria, wherein the predetermined criteria include thechange in reception conditions being of a magnitude such that the changein reception conditions cannot be coped with by the second signalamplifier.
 22. A radio receiver having at least one receiving signalpath with a first portion having an output coupled to an input of asecond portion, wherein the first portion comprises a first signalamplifier and the second portion comprises a second signal amplifier,the radio receiver comprising: a detector configured to detect a signalreception condition; and an Automatic Gain Control system, wherein theAutomatic Gain Control system comprises: a first AGC circuit comprising:circuitry coupled to receive a detection output from the detector andconfigured to initially control a gain of the first signal amplifierlocated in the first portion of the receiver and thereafter to controlthe gain of the first signal amplifier in response to detection of achange in reception conditions that satisfies predetermined criteria,wherein the first AGC circuit further comprises circuitry configured tocontrol the gain of the first signal amplifier in response to adetection that a first cycle time period has expired.